Apparatus for decoding a moving picture

ABSTRACT

Provided is an apparatus for decoding a moving picture. An inverse quantization/transformation unit generates a quantized block by inversely scanning a quantized coefficient sequence, generates a transform unit by inversely quantizing the quantized block using a quantization step size, and generates a residual block by inversely transforming the transform block. An inter prediction unit generates a prediction block of a current prediction unit based on motion vector information. An adding unit generates a restored block using the residual block and the prediction block. When a motion information coding mode is a skip mode, the inter prediction unit restores motion information of the current prediction block using an available spatial or temporal skip candidate The temporal skip candidate includes a reference picture index and a motion vector, the reference picture index of the temporal skip candidate is set to 0, and a motion vector of the temporal skip candidate is a motion vector of the temporal skip candidate in a temporal skip candidate picture. A size of the prediction unit is same with a size of a coding unit and the prediction block is set as the restored block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 14/812,157 filed on Jul. 29, 2015, which is a continuationapplication of U.S. application Ser. No. 13/624,814 filed on Sep. 21,2012, which is a continuation application of International ApplicationNo. PCT/KR2011/009562 filed on Dec. 13, 2011, which claims priority toKorean Application No. 10-2010-0127663 filed on Dec. 14, 2010 and KoreanApplication No. 10-2011-0064312 filed Jun. 30, 2011. The applicationsare incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to an apparatus for decoding a movingpicture, and more particularly, to an apparatus for constructing amotion vector list by using a candidate of a spatial motion vector and acandidate of a temporal motion vector, decoding a motion vector of acurrent prediction unit by using a received motion vector index, anddecoding the moving picture encoded in inter prediction mode.

BACKGROUND ART

In image compression methods such as Motion Picture Experts Group(MPEG)-1, MPEG-2, MPEG-4 and H.264/MPEG-4 Advanced Video Coding (AVC),one picture is divided into macroblocks to encode an image. And, therespective macroblocks are encoded using inter prediction or intraprediction. Then, an optimal coding mode is selected in the bases of adata size of a macroblock to be encoded and distortion of an originalmacroblock, and the macroblock is encoded.

In the inter prediction, a motion estimation is used to eliminatetemporal redundancy between consecutive pictures. The motion estimationcoding is a method which encodes an image by estimating and compensatinga motion of the current picture in the unit of block using one or morereference pictures.

In the motion estimation coding, the block most similar to the currentblock is searched within a predetermined search range for a referencepicture using a predetermined estimation function. If the most similarblock is searched, only residue between the current block and the mostsimilar block in the reference picture is transmitted to raise a datacompression ratio.

At this time, to decode the motion estimation coded current block,information for the motion vector indicating a position differencebetween the current block and the similar block in the referencepicture. Therefore, it is required to insert encoded information for themotion vector into a bitstream when the current block is encoded. Inthis process, if the information for the motion vector is encoded andinserted as it is, a compression ratio of an image data is decreasedbecause overhead is increased.

Therefore, in the inter prediction encoding, a motion vector of thecurrent block is predicted using blocks adjacent to the current block,only a difference value between the generated motion vector predictorand the original motion vector is encoded and transmitted, and theinformation of the motion vector is also compressed.

In H.264, the motion vector predictor, which is a predictor of a motionvector of the current block, is determined as a median of mvA, mvB andmvC. As neighboring blocks are inclined to be similar each other, themotion vector of the current block is determined as a median of themotion vectors of the neighboring blocks.

But, if one or more motion vectors of the neighboring blocks aredifferent from the motion of the current block, the median of the motionvectors of the neighboring blocks may be not an effective motion vectorpredictor for the current block. Also, a method of selecting a candidatefor predicting a motion vector and of encoding or decoding the motionvector more effectively compared to the known motion prediction methodis required when the motion of image is little or steady.

SUMMARY OF THE DISCLOSURE

The present invention is directed to provide an apparatus for decoding amotion vector of a current prediction unit using one of motion vectorsof a prediction unit adjacent to a current prediction unit and motionvectors located at a predetermined position in a different picturetimely.

One aspect of the present invention provides an apparatus for decoding amoving picture, comprising: an inverse quantization/transformation unitconfigured to generate a quantized block by inversely scanning aquantized coefficient sequence, generate a transform block by inverselyquantizing the quantized block using a quantization step size, andgenerate a residual block by inversely transforming the transform block;an inter prediction unit configured to generate a prediction block of acurrent block based on motion vector information; and an adding unitconfigured to generate a restored block using the residual block and theprediction block, wherein, when the prediction block is encoded in mergemode, the inter prediction unit restores motion information of thecurrent block using an available spatial or temporal skip candidate andgenerates the prediction block of the current block using the motioninformation, wherein the temporal merge candidate includes a referencepicture index and a motion vector, the reference picture index of thetemporal merge candidate is set to 0, and a motion vector of thetemporal merge candidate is a motion vector of the temporal mergecandidate in a temporal merge candidate picture, wherein, when thequantized block is larger than a predetermined size, the quantizationcoefficient sequence is generated by scanning a plurality of subsetsobtained by dividing the quantized block, and wherein a scan pattern forscanning the plurality of subsets is the same as a scan pattern forscanning quantized coefficients of each subset.

Preferably, the quantization step size is generated by adding aquantization step size predictor and a remaining quantization step sizepredictor, and when a quantization step sizes of a left coding unit andan above coding unit of the current block are unavailable, aquantization step size of a previous coding unit in a scan order isdetermined as the quantization step size of the current block.

Preferably, when the spatial skip candidate and the current predictionunit refer to different reference pictures and temporal distancesbetween the reference pictures are different, a motion vector of thespatial skip candidate is scaled.

An apparatus according to the present invention accurately decodes themotion vector of the current prediction unit, by which the motioninformation of the current prediction unit is effectively encoded, byusing available spatial motion vector candidates of prediction unitslocated at predetermined positions adjacent to the current predictionunit and one of temporal motion vector candidates of a prediction unitlocated at a position corresponding to the current prediction unit in areference picture encoded previously and located at a position adjacentto the position corresponding to the current prediction unit in thereference picture encoded previously. Therefore, computationalcomplexity and bandwidth of the decoder is reduced and the motioninformation is rapidly and accurately decoded.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating a method of scanning codingunits in a largest coding unit according to the present invention.

FIG. 2 is a block diagram of a moving picture coding apparatus accordingto the present invention.

FIG. 3 is a block diagram of a moving picture decoding apparatusaccording to the present invention.

FIG. 4 is a conceptual diagram illustrating positions of spatial skipcandidate blocks according to the present invention.

FIG. 5 is a conceptual diagram illustrating positions of blocks in atemporal skip candidate picture corresponding to a current predictionunit according to the present invention.

FIG. 6 is a conceptual diagram showing positions of neighboringprediction units used to generate motion vector candidates according tothe present invention.

DETAILED DESCRIPTION OF THE DISCLOSURE

Hereinafter, various embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.However, the present invention is not limited to the exemplaryembodiments disclosed below, but can be implemented in various types.Therefore, many other modifications and variations of the presentinvention are possible, and it is to be understood that within the scopeof the disclosed concept, the present invention may be practicedotherwise than as has been specifically described.

A picture is divided into a plurality of slices, and each slice isdivided into a plurality of largest coding units (LCUs). The position ofeach LCU is designated by an address indicator. The LCU may be a codingunit itself or may be divided into a plurality of coding units. The LCUcontains information indicating structure of coding units in the LCU.One or more split flags are used to indicate the structure of codingunits in the LCU.

Each coding unit (CU) consists of one or more prediction units. Theprediction unit is a basic unit for intra prediction or interprediction.

Each coding unit is composed of one or more prediction unit (PU). Atransform unit (TU) is a basic block for transform coding. In intraprediction, the prediction unit contains one or more transform units. Ininter prediction, a transform unit may be comprised of one or moreprediction units. The maximum size of the prediction unit is defined ina sequence parameter set (SPS), and the transform unit may be dividedinto a form of a recursive quad tree. The maximum size of the predictionunit in intra prediction may be different from that of the predictionunit in inter prediction. The maximum sizes of the prediction unit inintra prediction and inter prediction are contained the SPS.

A prediction unit structure of a coding unit for luminance component isthe same as that for chrominance components. But, a transform unitstructure of a coding unit for luminance component may be different fromthat for chrominance components. That is, the transform unit size of thechrominance component may be determined regardless of the transform unitsize of the luminance component. For example, the transform unit size ofthe chrominance component may be determined by the size of the codingunit. The transform unit size of the chrominance component may beadaptively adjusted by determining the maximum depth information of thechrominance component in advance. For example, if the depth informationof the luminance component is equal to or smaller than the depthinformation of the chrominance component, the transform unit of thechrominance component is divided according to division information ofthe transform unit of the luminance component. On the contrary, if thedepth information of the luminance component is larger than the depthinformation of the chrominance component, the transform unit of thechrominance component may be set not to have smaller size of the maximumdepth information of the transform unit of the chrominance component.The maximum depth information of the transform unit of the chrominancecomponent can be previously set or determined by the encoder andtransmitted to the decoder.

A procedure of scanning coding unit for decoding is as follows. First,an address of a LCU is parsed from the bit stream. A LCU size is alsoparsed. The LCU size may be a predetermined value between an encoder anda decoder, or may be inserted into a sequence header or a picture headerof a bit stream. A position of an upper left pixel of the LCU isobtained using the address and/or size of the LCU.

FIG. 1 is a conceptual diagram illustrating a method of scanning codingunits in a largest coding unit according to the present invention. Asshown in FIG. 1, the coding units in the LCU are scanned recursively inraster order.

If there are a plurality of prediction units in a coding unit, theprediction units are also scanned in raster order. The position of theprediction unit is specified by prediction unit index. Therefore theupper left pixel of the prediction unit is obtained using the predictionunit index.

If there are a plurality of transform units in a coding unit, theprediction units are also scanned recursively in raster order. The upperleft pixel of the transform unit is obtained using the transform unitindex.

Parameters transmitted by the encoder will be described. A sequenceparameter set (SPS) is transmitted through sequence header. The sequenceparameter set includes a smallest size of coding unit and maximum splitdepth information. The sequence parameter set also includes a smallestsize of transform unit and maximum transform depth information. Thetransform depth information may be different in intra prediction and ininter prediction.

A slice header includes a slice type. If the slice type is P or B,information indicating a method used to generate a prediction block isincluded. The slice header may include a flag indicating whether atemporal candidate is used or not when encoding motion information. Thetemporal candidate is a motion vector of the prediction unit whichexists at a position or nearby the position corresponding to theposition of the current prediction unit. It is possible that a pluralityof motion vectors exist at the position corresponding to the position ofthe current prediction unit or nearby or nearby the positioncorresponding to the position of the current prediction unit. In thiscase, one motion vector predetermined according to the position of thecurrent prediction unit is selected as a temporal motion vector. Theposition of the candidate may be changed according to a position of thecurrent prediction unit in LCU. The slice header may include a flagindicating whether a temporal candidate picture belongs to a referencepicture list 0 or a reference picture list 1. If there is not the flagindicating a reference picture list, a value of the flag is considered 1(that, the reference picture list 0).

The slice header includes information for managing memory to storereference pictures in case that the slice type is P or B.

The slice header includes a flag indicating whether adaptive loopfiltering is applied to the current slice. If the adaptive loopfiltering is applied, the slice header further includes adaptive loopfilter (ALF) parameter information. The ALF parameter informationincludes information indicating a horizontal filter length and/or avertical filter length of luminance components. The ALF parameterinformation may include information indicating the number of filters. Ifthe number of filters is 2 or more, the coefficients of the filter maybe encoded using prediction method. Furthermore, information whetherprediction method is used may be included in the slice header.

Chrominance components may also be filtered adaptively. The ALFparameter information may include information whether each chrominancecomponent is filtered or not. To reduce the amount of bits, theinformation indicating whether the Cr component is filtered andinformation indicating whether the Cb component is filtered may be codedjointly or multiplexed. An entropy coding is performed by assigning alowest index in case that both of Cr and Cb components are not filtered,because the probability that both of Cr and Cb components are notfiltered is high. And the information may include information indicatinga horizontal filter length and/or a vertical filter length ofchrominance components and filter information.

The ALF parameter may be transmitted in a picture header or anotherparameter set. In this case, the slice header does not include the ALFparameter and the ALF parameter may include index information indicatingthe ALF parameter.

The ALF process may be performed on the basis of coding unit or on thebasis of coding unit equal to or larger than a predetermined size. Andthe slice header may include information indicating whether the adaptiveloop filter process is applied to each coding unit. In this case, theinformation indicating the size of CU may be the predetermined size andmay be included in the slice header.

A slice includes a slice header and a plurality of LCUs. The LCUincludes information indicating the CU structure in the LCU. The CUstructure is a recursive quad tree structure. The CU structure mayinclude information (split_coding_unit_flag) which indicates whether apredetermined size of CU is split into smaller size of CUs. A codingunit of minimum size does not contain the split_coding_unit_flag. Acoding unit may include information (alf flag) indicating whether theALF is applied or not. If the alf_flag is not included, it is consideredthat the ALF is not applied. Therefore, the decoder determines whetherthe alf_flag is included and applies the loop filter adaptivelyaccording to the value of the alf_flag, if the alf_flag is included.

In H.264, a median value of a horizontal component and a verticalcomponent using motion vector of left neighboring block (A), an aboveneighboring block (B) and an above right neighboring block (C). But, inHEVC, because a prediction unit of adaptive size is used for motioncompensation, there is a high possibility that the size of the currentprediction unit is different from that of neighboring prediction unit.Therefore, the motion vector is predicted as follows.

A left motion vector which is located at and an above motion vector areused as spatial motion vector candidates. The left motion vector is amotion vector of one of a plurality of left neighboring prediction unitsand the above motion vector is a motion vector of one of a plurality ofabove neighboring prediction units. The neighboring prediction units maybe located at predetermined positions. For example, the left motionvector is an available motion vector encountered first when retrievingthe plurality of left neighboring prediction units in a firstpredetermined order, and the above motion vector is an available motionvector encountered first when retrieving the plurality of aboveneighboring prediction units in a second predetermined order. If acurrent prediction unit is located at the upper boundary of a picture ora slice, only the left motion vector is used as the spatial motionvector candidate. Also, if the current prediction unit is located at theleft boundary of a picture or slice, only the above motion vector isused as the spatial motion vector candidate.

A motion vector of a predetermined block is used as a temporal motionvector candidate. The predetermined block exists at or nearby a positionof a temporal candidate picture corresponding to a position of thecurrent prediction unit. A plurality of blocks may exist at or nearbythe position of a temporal reference picture candidate. Thus, thepredetermined block may be a block determined by a position of thecurrent prediction unit, or may be one of a plurality of blocks in apredetermined order. The predetermined block may be determined dependingon a position of the current prediction unit in a LCU of the currentprediction unit. In case that a slice including the current predictionunit is B slice, it is determined whether the temporal candidate picturecontaining the temporal motion vector candidate belongs to a referencepicture list 0 or 1. A list indicator indicating one reference picturelist is inserted in a slice header and transmitted to the decoder. Ifthe slice header does not contain the list indicator, the list indicatoris considered as 1 (that is, indicating reference picture list 0).

A procedure of encoding a motion vector of a current prediction unit isas follows.

First, a motion vector of the current prediction unit is obtained.

Next, an available left motion vector candidate and an available abovemotion vector candidate of the current prediction unit and neighboringthe current prediction unit are derived. If the motion vector ofneighboring prediction unit does not exist or the neighboring block ofthe current prediction unit exists outside of the boundary of thecurrent slice, the motion vector of the neighboring block is determinedas unavailable.

Next, the spatial motion vector candidate may be scaled adaptively. Ifthe current prediction unit and the neighboring prediction unit havesame reference picture, the motion vector candidate is not scaled. But,if the current prediction unit and the neighboring prediction unit havedifferent reference pictures and the temporal distances of the referencepictures are not same, the motion vector candidate may be scaled usingthe temporal distances. The motion vector may not be scaled for a stillimage or background image. In this case, information (flag) indicatingwhether scaling is applied or not may be transmitted to the decoder. Thenumber of scaling of the spatial motion vector candidate may be limitedto a predetermined number. For example, the number of scaling may be 1.In this case, if scaling is performed once, the second spatial motionvector candidate to be scaled is set as unavailable.

Next, an available temporal motion vector candidate is derived. Theavailable temporal motion vector candidate is the same as mentionedabove.

Next, a candidate list is constructed using the available spatial andtemporal motion vector candidates. The available temporal motion vectorcandidate is listed after the available spatial motion vector candidate.If a plurality of motion vector candidates are same, motion vectorcandidate of lower priority is deleted from the candidate list.

Next, a motion vector predictor of the current prediction unit isselected among the available spatial and temporal motion vectorcandidates. The number of motion vector candidate of the currentprediction unit may be predetermined. If the number of available motionvector candidates is larger than the predetermined number, the motionvector predictor of the current prediction unit is selected among thepredetermined number of motion vector candidates. If the number ofavailable motion vector candidates is smaller than the predeterminednumber, one or more additional motion vector candidates may be added.The additional motion vector candidate may be a zero vector.

Next, a motion vector difference is obtained and encoded. Informationindicating motion vector predictor is also encoded. The motion vectordifference is a difference between the motion vector of the currentprediction unit and the motion vector predictor of the currentprediction unit.

A procedure of decoding a motion vector of a current prediction unit isas follows.

A motion vector difference of the current prediction unit is decoded.

Information indicating a motion vector predictor of the currentprediction unit is restored.

Motion vector candidates for obtaining the motion vector predictor ofthe current prediction unit are determined through the followingprocedure.

First, an available left motion vector candidate and an available abovemotion vector candidate of the neighboring prediction unit of thecurrent prediction unit are derived. If the motion vector of theneighboring prediction unit does not exist or the neighboring block ofthe current prediction unit exists outside of the boundary of thecurrent slice, the motion vector of the neighboring block is determinedas unavailable.

Next, the spatial motion vector candidate may be scaled adaptively. Ifthe current prediction unit and the neighboring prediction unit havesame reference picture, the motion vector candidate is not scaled. But,if the current prediction unit and the neighboring prediction unit havedifferent reference pictures or the temporal distances of the referencepictures are not same, the motion vector candidate may be scaled usingthe temporal distances. The motion vector may not be scaled for a stillimage or background image. The number of scaling of the spatial motionvector candidate may be limited to a predetermined number. For example,the number of scaling may be 1. In this case, if scaling is performedonce, the second spatial motion vector candidate to be scaled is set asunavailable.

Next, an available temporal motion vector candidate is derived. Theavailable temporal motion vector candidate is the same as mentionedabove.

Next, a candidate list is constructed using the available spatial motionvector candidate and the available temporal motion vector candidate. Theavailable temporal motion vector candidate is listed after the availablespatial motion vector candidate. If a plurality of motion vectorcandidates are same, motion vector candidate of lower priority isdeleted from the candidate list.

Next, a motion vector predictor is selected among the available spatialmotion vector candidate and the available temporal motion vectorcandidate. The number of motion vector candidate may be predetermined Ifthe number of available motion vector candidates is larger than thepredetermined number, the motion vector predictor is selected among thepredetermined number of motion vector candidates. If the number ofavailable motion vector candidates is smaller than the predeterminednumber, one or more additional motion vector candidates may be added.The additional motion vector candidate is a zero vector.

When the motion vector candidates of the current prediction unit arederived, one motion vector candidate corresponding to informationindicating the motion vector predictor of the current prediction unit isdetermined as the motion vector predictor of the current predictionunit.

A motion vector of the current prediction unit is obtained using themotion vector difference and the motion vector predictor.

A reference picture index of the temporal candidate picture may be 0.

FIG. 2 is a block diagram of a moving picture coding apparatus 100according to the present invention.

Referring to FIG. 2, a moving picture coding apparatus 100 according tothe present invention includes a picture division unit 110, a transformunit 120, a quantization unit 130, a scanning unit 131, an entropycoding unit 140, an intra prediction unit 150, an inter prediction unit160, an inverse quantization unit 135, an inverse transform unit 125, apost-processing unit 170, a picture storing unit 180, a subtracter 190and an adder 195.

The picture division unit 110 divides analyzes an input video signal todivide each LCU of a picture into one or more coding units each of whichhas a predetermined size, determine prediction mode of each coding unit,and determines size of prediction unit per each coding unit. The picturedivision unit 110 sends the prediction unit to be encoded to the intraprediction unit 150 or the inter prediction unit 160 according to theprediction mode. Also, the picture division unit 110 sends theprediction units to be encoded to the subtracter 190.

The transform unit 120 transforms residual blocks which are residualsignals between an original block of a prediction unit and a predictionblock generated by the intra prediction unit 150 or the inter predictionunit 160. A size of a transform unit of the residual block is equal toor smaller than a size of coding unit. In intra prediction, the size ofthe transform unit is equal to or smaller than the size of theprediction unit. In inter prediction, the size of the transform unit isalso equal to or smaller than the size of the prediction unit, althoughthe size of the transform unit may be larger than the size of theprediction unit. A transform matrix may be adaptively determinedaccording to a prediction mode (intra or inter) and an intra predictionmode. The transform unit may be transformed by horizontal and verticalone-dimensional (1D) transform matrices.

In inter prediction, one predetermined transform matrix per eachtransform direction is applied.

If the prediction mode is intra prediction of luminance component andthe size of the transform unit is equal to or smaller than apredetermined size, the vertical and horizontal 1D transform matricesare adaptively determined. For example, if the intra prediction mode ishorizontal, there is a high possibility that the residual block willhave vertical directivity. Thus, a discrete cosine transform (DCT)-basedinteger matrix is applied to the vertical direction and a discrete sinetransform (DST) or Karhunen Loeve transform (KLT)-based integer matrixis applied to the horizontal direction. If the intra prediction mode isvertical, a DST or KLT-based integer matrix is applied to the verticaldirection and a DCT-based integer matrix is applied to the horizontaldirection. Also, in DC mode, a DCT-based integer matrix is applied tothe horizontal and vertical directions. That is, in intra prediction ofluminance component, the transform matrix may be adaptively determinedaccording to a size of the transform unit and the intra prediction mode.Meanwhile, in intra prediction mode of chrominance component, thetransform matrix is a predetermined matrix regardless of the predictionmode and the intra prediction mode.

Meanwhile, a transform pattern may adaptively be selected per transformunit among a plurality of transform patterns, and the selected transformpattern may be transmitted to a decoder. The plurality of transformpatterns may include a two-dimensional transform, a vertical transformand a horizontal transform. A scan pattern of the scanning unit 131 maybe determined by the transform pattern. For example, a first scanpattern (diagonal scan) is selected if the transform pattern is thetwo-dimensional transform, a second scan pattern (horizontal scan) isselected if the transform pattern is the vertical transform, a thirdscan pattern (vertical scan) is selected if the transform pattern is thehorizontal transform, and the first scan pattern is selected if thetransform pattern is the pattern where no transform is applied.

The quantization unit 130 determines a quantization step size forquantizing transform coefficients of the residual block transformed bythe transform matrix. The quantization step size is determined on acoding unit having a size equal to or larger than a predetermined size.For coding unit having a size smaller than the predetermined size, thequantization step size is determined on the predetermined size. Usingthe determined quantization step size and a quantization matrixdetermined according to a prediction mode, the transform coefficients ofthe transform block are quantized. When the size of the current codingunit is equal to or larger than the predetermined size, the quantizationunit 130 may determine a quantization step size predictor of the currentcoding unit using quantization step sizes of neighboring coding units ora quantization step size of a previous coding unit in scan order.

For example, the quantization unit 130 may determine a quantization stepsize of a left coding unit, a quantization step size of a above codingunit or average of the quantization step sizes of the left and abovecoding units as a quantization step size predictor according to an intraprediction mode of the current coding unit. If the above coding unitdoes not exist, the quantization step size of the left coding unit orthe previous coding unit may be determined as the quantization step sizepredictor. If the left coding unit is unavailable, the quantization stepsize of the above coding unit or the previous coding unit may bedetermined as the quantization step size predictor. When the average ofthe quantization step sizes of the left and the above coding units isused, if only one quantization step size is available, the available oneor the quantization step size of the previous coding unit may bedetermined as the quantization step size predictor. The above-mentionedmethod may be applied only to the coding unit within a LCU. That is, ifthe left or the above coding unit exists outside of the boundary of theLCU, the coding unit may be considered as a unavailable coding unit.

The quantized transform block is provided to the inverse quantizationunit 135 and the scanning unit 131.

The scanning unit 131 scans the coefficients of the quantized transformblock or information indicating whether the quantized transformcoefficients exists or not and transforms the coefficients and theinformation into 1D coefficients. A scan pattern is determined accordingto the prediction mode and the intra prediction mode. The scan patternmay also be determined according to the size of the transform unit.

The scanning unit 131 determines whether or not to divide the quantizedtransform block into a plurality of subsets according to the size of thecurrent transform unit. If the size of the transform unit is larger thana first reference size, the quantized transform block is divided intothe plurality of subsets. The first reference size is 4×4 or 8×8.

The scanning unit 131 determines a scan pattern to be applied to thequantized transform block. In inter prediction, a predetermined scanpattern (for example, zigzag scan) is used. In intra prediction, thescan pattern is selected based on the intra prediction mode and may bevaried according to a directional intra prediction mode. The first scanpattern is used for non-directional intra prediction modes. Thenon-directional intra prediction modes are a DC mode and a planar mode.The scan is performed in a forward direction or in a reverse direction.When the quantized coefficients are divided into a plurality of subsets,same scan pattern is applied to all the subsets. The plurality ofsubsets consist of one main subset and one or more residual subsets. Themain subset is located at an upper left side and includes a DCcoefficient. The one or more residual subsets cover region other thanthe main subset.

The first scan pattern may be applied to scan the subsets. The subsetsmay be scanned beginning with the main subset to the residual subsets ina forward direction, or can be scanned in a reverse direction. A scanpattern for scanning the subsets may be set the same as a scan patternfor scanning the quantized transform coefficients in the subsets. Inthis case, the scan pattern for scanning the subsets is determinedaccording to intra prediction mode.

An encoder transmits information capable of indicating a position of thelast non-zero quantized coefficient of the transform unit to a decoder.The encoder also transmits information capable of indicating a positionof the last non-zero quantized coefficient of each subset to the decoderor information indicating whether each subset includes non-zerocoefficient or not.

The inverse quantization unit 135 inversely quantizes the quantizedtransform coefficients. The inverse transform unit 125 restores residualblocks of the spatial domain from the inversely quantized transformcoefficients. The adder generates a reconstructed block by adding theresidual block reconstructed by the inverse transform unit 125 and theprediction block from the intra prediction unit 150 or the interprediction unit 160.

The post-processing unit 170 performs a deblocking filtering process forremoving blocking artifact generated in a reconstructed picture, anadaptive offset application process for complementing a differencebetween the reconstructed picture and the original image per pixel, andan adaptive loop filter process for complementing a difference betweenthe reconstructed picture and the original image in a coding unit.

The deblocking filtering process may be applied to a boundary betweenprediction units having a predetermined size or more and a boundarybetween transform units. The predetermined size may be 8×8. Thede-blocking filtering process includes a step of determining a boundaryto be filtered, a step of determining boundary filtering strength to beapplied to the boundary, a step of determining whether or not to apply adeblocking filter, and a step of selecting a filter to be applied to theboundary when it is determined to apply the de-blocking filter.

Whether or not to apply the deblocking filter is determined according toi) whether or not the boundary filtering strength is greater than 0 andii) whether or not a value indicating the difference between boundarypixels of P block and Q block is smaller than a first reference valuedetermined according to a quantization parameter.

Two or more filters may exist. When an absolute value of a differencebetween two pixels adjacent to the block boundary is equal to or largerthan a second reference value, a weak filter is selected. The secondreference value is determined by the quantization parameter and theboundary filtering strength.

The adaptive loop filter process may be performed on the basis of avalue obtained by comparing an original image and a reconstructed imageto which the de-blocking filtering process or the adaptive offsetapplication process is applied. An adaptive loop filter (ALF) isdetected through one Laplacian activity value on the basis of a 4×4block. The determined ALF can be applied to all pixels included in a 4×4block or an 8×8 block. Whether or not to apply an ALF may be determinedaccording to coding units. A size and coefficients of a loop filter mayvary according to each coding unit. A slice header may includeinformation indicating whether or not to apply the ALF to each codingunit, filter coefficient information and filter shape information, andso on. In the case of chrominance components, whether or not to applythe ALF may be determined in picture units. Unlike luminance, the loopfilter may have a rectangular shape.

The picture storing unit 180 receives post-processed image data from thepost-processing unit 160, and stores the image in picture units. Apicture may be an image in a frame or a field. The picture storing unit180 has a buffer (not shown) capable of storing a plurality of pictures.

The inter prediction unit 150 performs motion estimation using one ormore reference pictures stored in the picture storing unit 180, anddetermines reference picture indexes indicating the reference picturesand motion vectors. According to the reference picture index and themotion vector, the inter prediction unit 150 extracts a prediction blockcorresponding to a prediction unit to be encoded from a referencepicture selected among a plurality of reference pictures stored in thepicture storing unit 150 and outputs the extracted prediction block.

The intra prediction unit 140 performs intra prediction usingreconstructed pixel values within a current picture. The intraprediction unit 140 receives the current prediction unit to bepredictively encoded, selects one of a predetermined number of intraprediction modes, and performs intra prediction. The predeterminednumber of intra prediction modes may depend on the size of the currentprediction unit. The intra prediction unit adaptively filters thereference pixels to generate the intra prediction block. When some ofreference pixels are not available, it is possible to generate thereference pixels at the unavailable positions using one or moreavailable reference pixels.

The entropy coding unit 130 entropy-codes the quantized coefficientsquantized by the quantization unit 130, intra prediction informationreceived from the intra prediction unit 140, motion information receivedfrom the inter prediction unit 150, and so on.

FIG. 3 is a block diagram of a moving picture decoding apparatusaccording to the present invention.

Referring to FIG. 3, the moving picture decoding apparatus according tothe present invention includes an entropy decoding unit 210, an inversequantization/transform unit 220, an adder 270, a post-processing unit250, a picture storing unit 260, an intra prediction unit 230, an interprediction unit 240 and a switch 280.

The entropy decoding unit 210 extracts intra prediction mode indexes,motion vectors, quantized coefficients sequences (residual blocksignal), and so on from a received bit stream transmitted from a movingpicture coding apparatus. The entropy decoding unit 210 transmits thedecoded motion information to the inter prediction unit 240, the intraprediction mode indexes to the intra prediction unit 230 and the inversequantization/transform unit 220, and the quantized coefficients sequenceto the inverse quantization/transform unit 220.

The inverse quantization/transform unit 220 includes an inverse scanningunit 221, an inverse quantization unit 222 and an inverse transform unit223.

The inverse scanning unit 221 converts the quantized coefficientssequence into two dimensional inverse quantized coefficients. One of aplurality of inverse scan patterns is selected for the conversion. Theinverse scan pattern is selected based on at least one of the predictionmode (intra prediction mode or inter prediction mode) and the intraprediction mode of a current block.

For example, in inter prediction, a first scan pattern (for example,zigzag scan or diagonal scan) is used. In intra prediction, a secondscan pattern is selected based on the intra prediction mode. The secondscan pattern may be varied according to directional intra predictionmodes. For non-directional intra prediction modes, the first scanpattern may be applied.

If the size of a current transform unit to be decoded is larger than afirst predetermined reference size and the current transform unit isencoded in the unit of subsets, a quantized transform block is restoredby inversely scanning each subset. In this case, same scan pattern isapplied to all the subsets. The plurality of subsets consist of one mainsubset and one or more residual subsets. The main subset is located atan upper left side and includes a DC coefficient. The one or moreresidual subsets cover region other than the main subset.

The first scan pattern may be applied to inversely scan the subsets. Thesubsets may be scanned beginning with the main subset to the residualsubsets in a forward direction, or can be scanned in a reversedirection. A scan pattern for scanning the subsets may be set the sameas a scan pattern for scanning the quantized transform coefficients inthe subsets. In this case, the scan pattern for inversely scanning thesubsets is selected according to the intra prediction mode.

When the size of the transform unit is equal to or larger than apredetermined size, inverse scan may be performed by decodinginformation indicating whether each subset includes non-zerocoefficients. That is, the quantized transform block can be restored byinversely scanning coefficients in the subsets including non-zerocoefficients are inversely scanned using the information and by settingall the subsets including 0 as 0.

The inverse quantization unit 222 generates a quantization step sizepredictor of a current coding unit. The quantization step size isdetermined on a coding unit having a size equal to or larger than apredetermined size. If a plurality of coding units are included in thepredetermined size, the quantization step size is determined on thepredetermined size. The inverse quantization unit 222 may determine aquantization step size predictor using one or more quantization stepsizes of neighboring coding unit or a quantization step size of theprevious coding unit in scan order.

The inverse quantization unit 222 restores a quantization step size toinversely quantize the 2D inverse quantized coefficients. Thequantization step size is determined on a coding unit having a sizeequal to or larger than a predetermined size. If the size of codingunits is smaller than the predetermined size, the predeterminedquantization step size which is determined per each coding unit in theunit of the predetermined size is determined as the quantization stepsize. The inverse quantization unit 222 may use quantization step sizesof one or more neighboring coding units of the current prediction unitor a quantization step size of the previous coding unit in scan order asa quantization step size predictor of the current coding unit.

For example, the inverse quantization unit 222 may adaptively select aquantization step size of a left coding unit, a quantization step sizeof an above coding unit, or a rounded up average of quantization stepsized of the left and the above quantization step sizes as thequantization step size predictor of the current coding unit according tothe intra prediction mode of the current coding unit.

If the above coding unit does not exist, the quantization step size ofthe left coding unit or the previous coding unit may be determined asthe quantization step size predictor. If the left coding unit isunavailable, the quantization step size of the above coding unit or theprevious coding unit may be determined as the quantization step sizepredictor. When the rounded up average of the quantization step sizes ofthe left and the above coding units is used, if only one quantizationstep size is available, the available one or the quantization step sizeof the previous coding unit may be determined as the quantization stepsize predictor. In inter prediction, the quantization step sizepredictor is the rounded up average of the quantization step sizes ofthe left and the above coding units or the quantization step size of theprevious coding unit. Meanwhile, the above-mentioned method may beapplied only to the coding unit within a LCU. That is, if the left orthe above coding unit exists outside of the boundary of the LCU, thecoding unit may be considered as a unavailable coding unit.

When the quantization step size predictor is determined, thequantization step size of the current coding unit is generated by addinga received residual quantization step size and the quantization stepsize predictor. Then, the quantized transform coefficients are inverselyquantized using an inverse quantization matrix determined by thequantization step size and the prediction mode.

The inverse transform unit 223 determines an inverse transform matrixaccording to the size of the transform unit if the inverse quantizedblock is a luminance block and the prediction mode is intra. Forexample, if the size of the transform unit is equal to or smaller than apredetermined size, the vertical and the horizontal one-dimensionalinverse transform matrixes are determined according to the intraprediction mode. For example, if the intra prediction mode ishorizontal, there is a high possibility that the residual block willhave vertical directivity. Thus, a DCT-based integer matrix is appliedto the vertical direction, and a DST or KLT-based integer matrix isapplied to the horizontal direction. If the intra prediction mode isvertical, a DST or KLT-based integer matrix is applied to the verticaldirection, and a DCT-based integer matrix is applied to the horizontaldirection. Also, in DC mode, a DCT-based integer matrix is applied tothe horizontal and the vertical directions. That is, in intra predictionof luminance component, the inverse transform matrix may be adaptivelydetermined according to the size of the transform unit and the intraprediction mode. Meanwhile, in intra prediction mode of chrominancecomponent, the inverse transform matrix is a predetermined matrixregardless of the prediction mode (intra prediction mode or interprediction mode) and the intra prediction mode.

The adder 270 adds the restored residual block restored by the inversequantization/transform unit 220 and a prediction block generated by theintra prediction unit 230 or the inter prediction unit 240 to generate areconstructed block.

The post-processing unit 250 performs a deblocking filtering process forremoving blocking artifact generated in a reconstructed picture, anadaptive offset application process for complementing a differencebetween the reconstructed picture and the original image per pixel, andan adaptive loop filter process for complementing a difference betweenthe reconstructed picture and the original image in a coding unit.

The deblocking filtering process may be applied to boundaries ofprediction units and transform units having a predetermined size ormore. The deblocking filtering process may be applied to block edgehaving the size of 8×8 in case that the horizontal length or thevertical length of the prediction unit or the transform unit is smallerthan 8. The vertical edge is filtered first, and then the horizontaledge is filtered. The deblocking filtering process includes a step ofdetermining a boundary to be filtered, a step of determining boundaryfiltering strength to be applied to the boundary, a step of determiningwhether or not to apply a deblocking filter, and a step of selecting afilter to be applied to the boundary when it is determined to apply thedeblocking filter.

Whether or not to apply the deblocking filter is determined according toi) whether or not the boundary filtering strength is greater than 0 andii) whether or not a value indicating the difference between boundarypixels of P block and Q block is smaller than a first reference valuedetermined according to a quantization parameter.

Two or more filters may exist. When an absolute value of a differencebetween two pixels adjacent to the block boundary is equal to or largerthan a second reference value, a weak filter is selected. The secondreference value is determined by the quantization parameter and theboundary filtering strength.

The adaptive loop filter process may be performed on the basis of avalue obtained by comparing an original image and a reconstructed imageto which the de-blocking filtering process or the adaptive offsetapplication process is applied. An adaptive loop filter (ALF) isdetected through one Laplacian activity value on the basis of a 4×4block. The determined ALF can be applied to all pixels included in a 4×4block or an 8×8 block. Whether or not to apply an ALF may be determinedaccording to coding units. A size and coefficients of a loop filter mayvary according to each coding unit. A slice header may includeinformation indicating whether or not to apply the ALF to each codingunit, filter coefficient information and filter shape information, andso on. In the case of chrominance components, whether or not to applythe ALF may be determined in picture units. Unlike luminance, the loopfilter may have a rectangular shape.

The picture storing unit 260 is a frame memory storing a localreconstructed picture filtered by the post-processing unit 250.

The intra prediction unit 230 restores the intra prediction mode of thecurrent block based on the received intra prediction mode index, andgenerates a prediction block according to the restored intra predictionmode.

The switch 280 provides a prediction unit generated by the intraprediction unit 230 or the inter prediction unit 240 to the adder 270according to the prediction mode.

The inter prediction unit 240 restores motion information of the currentprediction unit based on the received motion information, and generatesa prediction block from the picture stored in the picture storing unit260 based on the restored motion information. When motion compensationof decimal precision is applied, the inter prediction unit 240 generatesthe prediction block by applying a selected interpolation filter.

Now, a method of decoding a moving image in inter prediction mode isdescribed. The method comprises a procedure of generating a predictionblock of the current prediction unit, a procedure of restoring aresidual block of the current prediction unit and a procedure ofgenerating a reconstructed block using the prediction block and theresidual block. The procedure of generating a prediction block isperformed by the inter prediction unit 240 of FIG. 3.

The procedure of generating a prediction block of a current predictionunit is as follows. The procedure includes 1) a step for deriving motioninformation of a prediction unit and 2) a step for generating aprediction block of the prediction unit. The motion information includesmotion vector, prediction direction and reference picture index.

When the prediction unit is encoded in skip mode, the procedure ofgenerating a prediction block is as follows. If a skip_flag in areceived coding unit is 1, the prediction unit is the coding unit.

FIG. 4 is a conceptual diagram showing positions of spatial skipcandidates according to the present invention. As shown in FIG. 4, aleft prediction unit (block A), an above prediction unit (block B), anabove right prediction unit (block C) and a left below prediction unit(block D) may be the spatial skip candidates. When a plurality of leftprediction units exist, an uppermost left prediction unit or a lowestleft prediction unit may be determined as the left prediction unit. Whena plurality of above prediction units exist, a leftmost above predictionunit or a rightmost above prediction unit may be determined as the aboveprediction unit.

First, the availability of each spatial skip candidate (A, B, C, D) ischecked. If the prediction unit does not exist or the prediction mode ofthe prediction unit is intra, the candidate block is determined asunavailable.

The above left prediction unit (block E) of the current prediction unitcan be a spatial skip candidate if one or more than a predeterminednumber of the candidate blocks A, B, C and D are unavailable. Thepredetermined number may be decided according to the number of skipcandidates transmitted from an encoder.

A temporal skip candidate is derived. The procedure of deriving thetemporal skip candidate includes a step for deriving a reference pictureindex of the temporal skip candidate and a step for deriving a motionvector of the temporal skip candidate. The reference picture index oftemporal skip candidate may be set to 0 or may be derived usingreference picture indexes of spatially neighboring prediction units. Theneighboring prediction units are predetermined.

The motion vector for the temporal skip candidate is derived as follows.

First, a picture (hereinafter, ‘a temporal skip candidate picture’)which a temporal skip candidate block belongs to is determined. Areference picture of index 0 may be determined as the temporal skipcandidate picture. For example, a first reference picture of thereference picture list 0 is determined as the temporal skip candidatepicture when the slice type is P. When the slice type is B, onereference picture list is selected using a flag of slice headerindicating the temporal skip candidate picture and a first referencepicture of the selected reference picture list is determined as thetemporal skip candidate picture. For example, the temporal skipcandidate picture is derived from the selected reference picture list 0when the flag is 1, whereas, the temporal skip candidate picture isderived from the selected reference picture list 1 when the flag is 0.

Alternatively, a reference picture indicated by a reference pictureindex for temporal skip candidate is determined as the temporal skipcandidate picture which the temporal skip candidate block belongs to.

Next, a temporal skip candidate block is derived. One of a plurality ofblocks corresponding to the current prediction unit is selected as thetemporal skip candidate block. The plurality of blocks are included inthe temporal skip candidate picture. In this case, one of a plurality ofblocks is selected based on a position of the current prediction unit orone of a plurality of blocks located at a predetermined position isselected. When one of a plurality of blocks is selected, a firstavailable block determined based on the priorities assigned to theplurality of blocks is selected as the temporal skip candidate block. Ifthe motion vectors of the blocks corresponding to the current predictionunit are not available, the temporal skip candidate is considered asunavailable.

FIG. 5 is a conceptual diagram illustrating positions of blocks in atemporal skip candidate picture corresponding to a current predictionunit according to the present invention.

In a case of selecting one of the candidate blocks, a below right cornerblock (block BR_C) or a lower right block (block BR) may be a first skipcandidate block. And a block (block C1) including an upper left pixel ora block (block C2) including an upper left pixel of the center positionof a block which is included in the temporal skip candidate picture andcorresponds to the current prediction unit may be a second skipcandidate block. If the first candidate block is available, the firstcandidate block is determined as the temporal skip candidate block. Ifthe first candidate block is not available and the second candidateblock is available, the second candidate block is determined as thetemporal skip candidate block.

When the current prediction unit is located at the lower boundary orright boundary of a picture, the second candidate block is determined asthe temporal skip candidate block if the second skip candidate block isavailable. When the current prediction unit is located at the lowerboundary of a slice or a LCU, the second candidate block is determinedas the temporal skip candidate block if the second candidate block isavailable.

Next, a skip candidate list is generated.

The skip candidate list is generated using available spatial andtemporal skip candidates. The skip candidates may be listed in apredetermined order. The predetermined order may be an order of aspatial left skip candidate (block A), a spatial above skip candidate(block B), a temporal skip candidate, a spatial above right skipcandidate (block C) and a spatial below left skip candidate (block D).

The predetermined order may be changed according to the number of skipcandidates transmitted from an encoder. In this case, the order ofspatial skip candidates is not changed (that is, A, B, C, D, E, andavailable spatial skip candidates are allowed), but the priority of thetemporal skip candidate may be changed. For example, if the number ofskip candidates is 5, the temporal skip candidate is listed afteravailable spatial skip candidates. If the number of skip candidates is3, the order of a temporal skip candidate may be adjusted so that thetemporal candidate is listed in top 3. The skip candidates may be listedin an order of the spatial left skip candidate (block A), the spatialabove skip candidate (block B) and the temporal skip candidate. If twoor more available spatial skip candidates exist, the temporal skipcandidate is listed after two of available spatial skip candidates. Whenthe number of skip candidates is 2 or 4, the same method is applied.

Meanwhile, if the number of the available skip candidates in the skipcandidate list is smaller than a received candidate number from theencoder, one or more skip candidate are generated. The generated skipcandidate is listed after the last available skip candidate. When aplurality of skip candidates are generated, the candidates are added ina predetermined order.

The skip candidates are generated using a plurality of methods in apredetermined order. The method used to generate the skip candidatedepends on the type of slice to which the current prediction unitbelongs.

When a current slice type is B and the number of available skipcandidates is two or more, a first method may be used. When thereference list of the first available skip candidate is different fromthe reference list of the second available skip candidate, the motioninformation of the first available skip candidate and the motioninformation of the first available skip candidate may be combined togenerate one or more skip candidates. The generated skip candidate isbi-directional motion information. If a plurality of skip candidates aregenerated, the generated skip candidates are added according to apredetermined order. The predetermined order is determined based onindexes of the available skip candidates. The number of the skipcandidates generated by the first method may be limited to apredetermined number.

In a second method, a skip candidate having zero motion vector is added.The skip candidate having zero motion vector is one of a uni-directionalL0 skip candidate, a uni-directional L1 skip candidate and abi-directional skip candidate. The uni-directional L0 skip candidate haszero motion vector, reference picture list 0 and reference picture indexof 0. The uni-directional L1 skip candidate has zero motion vector,reference picture list 1 and reference picture index of 0. Thebi-directional skip candidate is a combination of the uni-directional L0skip candidate and the uni-directional L1 skip candidate.

When the current slice type is P, the uni-directional L0 skip candidateis added. When the current slice type is B, one or more skip candidateshaving zero motion vector may be added. For the slice type B, thebi-direction skip candidate may be added first or skip candidates havingzero motion vector may be added in a predetermined order (for example,in an order of the bi-directional skip candidate and the uni-directionalskip candidate) until the number of skip candidate is reached.

Next, the motion vector and the reference picture index of the currentprediction unit are derived.

When there is a skip index in the received prediction unit, the motionvector and the reference picture index of the skip candidate indicatedby the skip index are determined as the motion vector and the referenceindex of the current prediction unit. When there is not a skip index inthe received prediction unit and there exists a skip candidate, themotion vector and the reference picture index of the skip candidate aredetermined as the motion vector and the reference index of the currentprediction unit. When the skip index indicates the temporal skipcandidate, the motion vector of the temporal skip candidate isdetermined as the motion vector of the current prediction unit and thereference picture index for the temporal skip candidate is determined asthe reference picture index of the current prediction unit.

If the motion vector and the reference picture index of the currentprediction unit are derived, a prediction block is generated usingmotion vector in the picture indicated by the reference picture index.The prediction block is output as a reconstructed block of the currentprediction unit.

Next, merge mode is described.

When the skip_flag in the coding unit is 0 and merge_flag in thereceived prediction unit is 1, a procedure of generating a predictionblock is almost same as the procedure of generating a prediction blockof the skip mode.

Available spatial merge candidates are derived from neighboringprediction units. The procedure for obtaining the spatial mergecandidates is the same as the spatial skip candidates. But, when thecurrent prediction unit is 2N×N, N×2N, 2N×nU, 2N×nD, nL×2N or nR×2N andthe current prediction unit is a partition 1, the merge candidatecorresponding partition 0 is deleted.

The procedure for obtaining the temporal merge candidate is the same asthe temporal skip candidate.

A procedure of constructing a merge candidate list and a procedure ofgenerating merge candidate are the same as the procedures in the skipmode.

When there is a merge index in the received prediction unit, the motionvector and the reference picture index of the merge candidate indicatedby the merge index in the merge candidate list are determined as themotion vector and the reference index of the current prediction unit.When there is not a merge index in the received prediction unit, themotion vector and the reference picture index of the first availablemerge candidate are determined as the motion vector and the referenceindex of the current prediction unit.

If the motion vector and the reference picture index of the currentprediction unit are derived, a prediction block is generated using themotion vector in the picture indicated by the reference picture index.

Next, a residual block is restored from a received residual signalthrough entropy decoding, inverse scan, inverse quantization and inversetransform. The procedures are performed by the entropy decoding unit210, the inverse scanning unit 221, the inverse quantization unit 222and the inverse transform unit 223 of the decoding apparatus of FIG. 3,respectively.

Finally, a reconstructed block of the current prediction unit isgenerated using the prediction block and the residual block.

Next, AMVP mode will be described. When the skip_flag in a coding unitis 0 and the merge_flag in a received prediction unit is 0, AMVP mode isapplied. The procedure of generating the prediction block is as follows.

First, a reference picture index and a motion vector difference of acurrent prediction unit are obtained from the received bit stream. Ifslice type is B, inter prediction information (inter_pred_flag) ischecked. If the inter prediction information indicates a uni-directionalprediction using combined reference picture list (Pred_LC), a referencepicture among the reference pictures of the combined reference picturelist (list_c) is selected using the reference picture index, and themotion vector difference is restored. If the inter predictioninformation indicates a uni-directional prediction using a referencepicture list 0, a reference picture is selected using the referencepicture index of the reference picture list 0, and the motion vectordifference is restored. If the inter prediction information indicates anbi-directional prediction, each reference picture is selected using eachreference picture index of the reference picture lists 0 and 1, and eachmotion vector difference for each reference picture is restored.

Next, a motion vector prediction is determined. The motion vectorpredictor is selected among the spatial motion vector candidates and thetemporal motion vector candidate.

FIG. 6 is a conceptual diagram showing positions of neighboringprediction units used to generate motion vector candidates according tothe present invention.

A spatial left motion vector candidate may be one of left predictionunits (one of blocks A₀ and A₁) of a current prediction unit. A spatialabove motion vector candidate may be one of above prediction units(blocks B₀, B₁ and B₂) of the current prediction unit.

First, a procedure for deriving the spatial left motion vector candidatewill be described.

It is checked whether there is a prediction unit satisfying firstconditions or second conditions by retrieving the left blocks of thecurrent prediction unit in the order of blocks A₀ and A₁. The firstconditions are 1) there exists a prediction unit, 2) the prediction unitis an inter prediction coded unit, 3) the prediction unit has samereference picture as that of the current prediction unit and 4) theprediction unit has same reference picture list as that of the currentprediction unit. If there is a prediction unit satisfying the firstconditions, the motion vector of the prediction unit is determined asthe spatial left motion vector candidate. The second conditions are 1)there exists a prediction unit, 2) the prediction unit is an interprediction coded unit, 3) the prediction unit has same reference pictureas that of the current prediction unit and 4) the prediction unit hasdifferent reference picture list from that of the current predictionunit. If there is a prediction unit satisfying the second conditions,the motion vector of the prediction unit is determined as the spatialleft motion vector candidate. If there is a prediction unit satisfyingthe first conditions or the second conditions, the motion vector of theprediction unit is determined as the spatial left motion vectorcandidate.

If there does not exist a prediction unit satisfying any one of thefirst conditions and the second conditions, it is checked whether thereis a prediction unit satisfying third conditions or fourth conditionswhen retrieving the left blocks in the order of blocks A₀ and A₁. Thethird conditions are 1) there exists a prediction unit, 2) theprediction unit is an inter prediction coded unit, 3) the predictionunit has same reference picture list as that of the current predictionunit and 4) the prediction unit has different reference picture fromthat of the current prediction unit. If there is a prediction unitsatisfying the third conditions, the motion vector of the predictionunit is determined as the spatial left motion vector candidate. Thefourth conditions are 1) there exists a prediction unit, 2) theprediction unit is an inter prediction coded unit, 3) the predictionunit has different reference picture list from that of the currentprediction unit and 4) the prediction unit has different referencepicture from that of the current prediction unit. If there is aprediction unit satisfying the third conditions or the forth conditions,the motion vector of the prediction unit is determined as the spatialleft motion vector candidate.

The motion vector of the prediction unit satisfying the first conditionsor the second conditions is not scaled. But, the motion vector of theprediction unit satisfying the third conditions or the forth conditionsis scaled.

If there is not a prediction unit satisfying any one conditions, thespatial left motion vector candidate is unavailable.

A procedure for deriving a spatial above motion vector candidate is asfollows.

It is checked whether there is a prediction unit satisfying the firstconditions or the second conditions when retrieving the above blocks inthe order of blocks B₀, B₁ and B₂. If there is a prediction unitsatisfying the first conditions or the second conditions, the motionvector of the prediction unit is determined as the spatial above motionvector candidate.

If there does not exist a prediction unit satisfying any one of thefirst conditions and the second conditions, it is checked whether thereis a prediction unit satisfying third conditions or fourth conditions.If there is a prediction unit satisfying the third conditions or theforth conditions, the motion vector of the prediction unit is determinedas the spatial left motion vector candidate. But, If the spatial leftmotion vector candidate is satisfying the third conditions or the forthconditions, the spatial above motion vector candidate may be set to beunavailable.

The procedure of deriving a temporal motion vector candidate is the sameas that of the motion vector of the temporal skip candidate.

Next, a motion vector candidate list is constructed.

The motion vector candidate list is constructed using available spatialand temporal motion vector candidates. The motion vector candidate listmay be constructed in a predetermined order. The predetermined order isthe order of a spatial left motion vector candidate (block A), a spatialabove motion vector candidate (block B) and a temporal motion vectorcandidate, or the order of a temporal motion vector candidate, a spatialleft motion vector candidate (block A) and a spatial above motion vectorcandidate (block B).

The predetermined order may be changed according to a prediction mode ofthe prediction unit.

Next, if a plurality of candidates have same motion vector, thecandidate having lower priority is deleted in the motion vectorcandidate list. If the number of motion vector candidates in the list issmaller than a predetermined number, a zero vector is added.

Next, a motion vector predictor of the current prediction unit isobtained. The motion vector candidate indicated by the motion vectorindex is determined as the motion vector predictor of the currentprediction unit.

Next, a motion vector of the current prediction unit is generated byadding the motion vector difference received from an encoder and themotion vector predictor. And a prediction block is generated using thereference picture index received from the encoder and the restoredmotion vector

Also, a residual block is restored from a residual signal received fromthe encoder through entropy decoding, inverse scan, inverse quantizationand inverse transform. The procedures are performed by the entropydecoding unit 210, the inverse scanning unit 221, the inversequantization unit 222 and the inverse transform unit 223 of the decodingapparatus of FIG. 3, respectively.

Finally, a reconstructed block is generated using the prediction blockand the residual block

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. An apparatus for decoding a moving picture, the apparatus comprising:an inverse quantization/transformation unit configured to generate aquantized block by inversely scanning a quantized coefficient sequence,generate a transform unit by inversely quantizing the quantized blockusing a quantization step size, and generate a residual block byinversely transforming the transform block; an inter prediction unitconfigured to generate a prediction block of a current prediction unitbased on motion vector information; and an adding unit configured togenerate a restored block using the residual block and the predictionblock, wherein, when a motion information coding mode is a skip mode,the inter prediction unit restores motion information of the currentprediction block using an available spatial or temporal skip candidateand generates the prediction block of the current prediction unit usingthe motion information, wherein the temporal skip candidate includes areference picture index and a motion vector, the reference picture indexof the temporal skip candidate is set to 0, and a motion vector of thetemporal skip candidate is a motion vector of the temporal skipcandidate in a temporal skip candidate picture, and wherein a size ofthe prediction unit is same with a size of a coding unit and theprediction block is set as the restored block.
 2. The apparatus of claim1, wherein, when the quantized block is larger than a predeterminedsize, the quantization coefficient sequence is generated by scanning aplurality of subsets obtained by dividing the quantized block.
 3. Theapparatus of claim 2, wherein a scan pattern for scanning the pluralityof subsets is same with a scan pattern for scanning quantizedcoefficients of each subset.
 4. The apparatus of claim 1, wherein thequantization step size is generated by adding a quantization step sizepredictor and a remaining quantization step size predictor and when aquantization step sizes of a left coding unit and an above coding unitof the current prediction unit are unavailable, a quantization step sizeof a previous coding unit in a scan order is determined as thequantization step size of the current prediction unit.
 5. The apparatusof claim 1, wherein, when the spatial skip candidate and the currentprediction unit refer to different reference pictures and temporaldistances between the reference pictures are different, a motion vectorof the spatial skip candidate is scaled.